1. Field Teachings
The present teachings relate, generally, to differentials, and more specifically to a differential having light weight bevel gearing.
2. Description of the Related Art
Differentials are well known devices used in vehicle drive trains. These devices operate to couple a pair of rotating members, such as drive shafts or axle half shafts about a rotational axis. Thus, differentials have been employed as a part of transfer cases that operatively couple the front and rear axles of a vehicle, in open differentials as well as limited slip and locking differentials used to couple axle half shafts, and other applications commonly known in the art.
Differentials of the type known in the related art may include a housing and a gear case that is operatively supported by the housing for rotation by a vehicle drive train. The differential typically includes at least a pair of side gears. The side gears are splined for rotation with a pair of rotating members, such as axle half shafts. A spider having cross pins is operatively mounted for rotation with the gear case. Pinion gears are mounted for rotation with the cross pins and in meshing relationship with the side gears. Differential rotation of the side gears and thus the axle half shafts may be obtained through rotation of the pinion gears relative to the cross pins as is commonly known in the art.
In all practical designs of intersected-axis gearing, for example, in straight bevel gearing, spiral bevel gearing, etc., the side gear teeth are stronger, while the pinion gear teeth are weaker. This is due to the difference in tooth count in the side gear and in the pinion gear: the larger the tooth count, the stronger gear tooth and vice versa. Therefore, to increase power density through the gear set, it is required first to take care of the pinion gear (teeth of which are weaker) and not of the mating side gear (teeth of which are stronger). Moreover, it is common to sacrifice a portion of strength of the side gear teeth in order to increase the strength of the pinion gear teeth. In an ideal case, strength of the side gear teeth and strength of the pinion gear teeth are equal to one another.
It is shown (see, for example a monograph: Radzevich, S. P., Theory of Gearing: Kinematics, Geometry, and Synthesis, CRC Press, Boca Raton Fla., 2012, 856 pages), that the power, P, being transmitted by a gear pair is shared equally within a face width of the gear tooth. Assume that a pinion gear in a gear set is sliced on a large number of equally thin slices each of which is perpendicular to the pinion gear axis of rotation. As all the slices are of equal thickness, then equal power is transmitting through each slice.
Power, P, being transmitting by a pinion gear can be expressed in terms of the applied torque, T, and of the rotation of the pinion gear, R,P=T*R (1)
After being sliced, all the pinion gear slices have the same rotation, R. As the rotations of all the slices are equal, then the torque being transmitting is also shared equally within a face width of the pinion gear.
While differentials of the type generally known in the art and as described above have worked for their intended purposes, certain disadvantages remain. More specifically, there remains ongoing and continuous efforts to improve the operation of such differentials. One disadvantage associated with such differentials is the use of bevel gears with straight teeth for the mating surfaces between the pinion gears and the side gears. Due to both the side gears and pinion gears being beveled, an axial thrust is exerted in the pinion-to-side gear mesh acting outwards of the centerline of the axes. This creates an additional load onto the differential case and results in a relatively heavy weight of the differential case to withstand the load. Power density through the differential is limited by the geometry of contact of the interacting teeth flanks of the side gear and of the pinion gear.
Thus, there remains a need in the art for a differential that allows for the smooth meshing interaction between the pinion gears and its associated side gears to increase power density through the differential while reducing weight of the differential.